linux-kernel - Re: [PATCH 2/2] net: dsa: microchip: Provide Module 4 KSZ9477 errata (DS80000754C)

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Message-ID: <20230829103533.7966f332@wsk>
Date:   Tue, 29 Aug 2023 10:35:33 +0200
From:   Lukasz Majewski <lukma@...x.de>
To:     Vladimir Oltean <olteanv@...il.com>, Tristram.Ha@...rochip.com
Cc:     f.fainelli@...il.com, andrew@...n.ch, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, Woojung.Huh@...rochip.com,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH 2/2] net: dsa: microchip: Provide Module 4 KSZ9477
 errata (DS80000754C)

Hi Vladimir,

> On Fri, Aug 25, 2023 at 06:48:41PM +0000, Tristram.Ha@...rochip.com
> wrote:
> > > > IMHO adding functions to MMD modification would facilitate
> > > > further development (for example LED setup).  
> > > 
> > > We already have some KSZ9477 specific initialization done in the
> > > Micrel PHY driver under drivers/net/phy/micrel.c, can we converge
> > > on the PHY driver which has a reasonable amount of infrastructure
> > > for dealing with workarounds, indirect or direct MMD accesses
> > > etc.?  
> > 
> > Actually the internal PHY used in the KSZ9897/KSZ9477/KSZ9893
> > switches are special and only used inside those switches.  Putting
> > all the switch related code in Micrel PHY driver does not really
> > help.  When the switch is reset all those PHY registers need to be
> > set again, but the PHY driver only executes those code during PHY
> > initialization.  I do not know if there is a good way to tell the
> > PHY to re-initialize again.  
> 
> Suppose there was a method to tell the PHY driver to re-initialize
> itself. What would be the key points in which the DSA switch driver
> would need to trigger that method? Where is the switch reset at
> runtime?

Tristam has explained why adding the internal switch PHY errata to
generic PHY code is not optimal.

If adding MMD generic code is a problem - then I'm fine with just
clearing proper bits with just two indirect writes in the
drivers/net/dsa/microchip/ksz9477.c

I would also prefer to keep the separate ksz9477_errata() function, so
we could add other errata code there.

Just informative - without this patch the KSZ9477-EVB board's network
is useless when the other peer has EEE enabled by default (like almost
all non managed ETH switches).



Best regards,

Lukasz Majewski

--

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